Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) Release 8+ operating with a single serving cell (hereafter LTE R8+) supports up to 100 Mbps in the downlink (DL), and 50 Mbps in the uplink (UL) for a 2×2 configuration. The LTE downlink transmission scheme is based on an orthogonal frequency division multiple access (OFDMA) air interface. For the purpose of flexible deployment, LTE R8+ systems support scalable transmission bandwidths, one of 1.4, 2.5, 5, 10, 15, or 20 MHz.
In LTE R8+, each radio frame (10 ms) includes 10 equally sized sub-frames of 1 ms. Each sub-frame includes 2 equally sized timeslots of 0.5 ms each. There can be either seven or six orthogonal frequency division multiplexing (OFDM) symbols per timeslot. Seven symbols per timeslot are used with normal cyclic prefix length, and six symbols per timeslot can be used in an alternative system configuration with the extended cyclic prefix length. The sub-carrier spacing for the LTE R8/9 system is 15 kHz. An alternative reduced sub-carrier spacing mode using 7.5 kHz is also possible.
A resource element (RE) corresponds to one (1) sub-carrier during one (1) OFDM symbol interval. Twelve (12) consecutive sub-carriers during a 0.5 ms timeslot constitute one (1) resource block (RB). With seven (7) symbols per timeslot, each RB includes 12×7=84 REs. A DL carrier may consist of scalable number of resource blocks (RBs), ranging from a minimum of six (6) RBs up to a maximum of 110 RBs. This corresponds to an overall scalable transmission bandwidth of roughly 1 MHz up to 20 MHz. However, usually a set of common transmission bandwidths is specified, for example, 1.4, 3, 5, 10 or 20 MHz.
The basic time-domain unit for dynamic scheduling is one sub-frame including two consecutive timeslots. This is sometimes referred to as a resource-block pair. Certain sub-carriers on some OFDM symbols are allocated to carry pilot signals in the time-frequency grid. A given number of sub-carriers at the edges of the transmission bandwidth are not transmitted in order to comply with spectral mask requirements.